Pendulum stabilization for antenna structure with padome

ABSTRACT

Tactical radio navigation systems provide bearing, distance and identification determining signals generated by a reply transmitter as emitted from an antenna structure. Antenna structures mounted on movable platforms, such as a ship&#39;&#39;s mast, must be position stabilized to provide maximum power to the bearing and distance signals above the horizon. To stabilize the antenna structure, a supporting yoke mounts to the movable platform. This yoke supports bearings aligned along an axis to provide stabilization in a given direction. Mounted to these bearings are journals extending from the mounting plate of an antenna pedestal. The plate supports the central array of the antenna structure and has a spin motor attached to the underside thereof. This spin motor acts like a pendulum to stabilize the pedestal with reference to the horizon around the desired stabilization direction. Mounted to the output shaft of the spin motor are parasitic elements which rotate around the antenna structure to provide a modulation frequency. When two degrees of stabilization are required, a gimbal ring mounts to the supporting yoke and the pedestal mounts to the gimbal ring. In systems where multiple degrees of stabilization are required, bearings of the yoke are aligned along an axis in the first direction of desired stabilization and bearings of the gimbal ring are aligned along an axis in the second direction of desired stabilization.

United States Patent [191 Bauer et a1.

[ Jan. 29, 1974 1 PENDULUM STABILIZATION FOR ANTENNA STRUCTURE WITH RADOME [75] Inventors: George B. Bauer, Reston, Va.; Dean S. Thornberg, Salt Lake City, Utah [73] Assignee: E-Systems Inc., Dallas, Tex. by said Thornberg [22] Filed: July 19, 1972 [21] Appl. No.: 273,304

[30] Foreign Application Priority Data Primary ExaminerE1i Lieberman [5 7] ABSTRACT Tactical radio navigation systems provide bearing, distance and identification determining signals generated by a reply transmitter as emitted from an antenna structure. Antenna structures mounted on movable platforms, such as a ships mast, must be position stabilized to provide maximum power to the bearing and distance signals above the horizon. To stabilize the antenna structure, a supporting yoke mounts to the movable platform. This yoke supports bearings aligned along an axis to provide stabilization in a given direction. Mounted to these bearings are journals extending from the mounting plate of an antenna pedestal. The plate supports the central array of the antenna structure and has a spin motor attached to the underside thereof. This spin motor acts like a pendulum to stabilize the pedestal with reference to the horizon around the desired stabilization direction. Mounted to the output shaft of the spin motor are parasitic elements which rotate around the antenna structure to provide a modulation frequency. When two degrees of stabilization are required, a gimbal ring mounts to the supporting yoke and the pedestal mounts to the gimbal ring. In systems where multiple degrees of stabilization are required, bearings of the yoke are aligned along an axis in the first direction of desired stabilization and bearings of the gimbal ring are aligned along an axis in the second direction of desired stabilization.

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PENDULUM STABILIZATION FOR ANTENNA STRUCTURE WITH PADOME This invention relates to position stabilized antenna structures, and more particularly to pendulum stabilized antenna structures.

Tactical radio navigation systems provide distance measuring information to an interrogating aircraft in response to pairs of interrogation pulses received at a beacon transponder; such systems also provide bearing and identification information. The transponder receives pairs of interrogation pulses which are decoded into a single pulse for operation of a reply transmitter. Bearing, distance and identification determining signals are generated by the reply transmitter at its antennas. A single antenna functions to both receive the interrogation pulses and radiate the position determining signals. To provide the required bearing information, the antenna radiates pulses from a central antenna array that is stationary with respect to a support housing. These pulses are modulated at a Hz frequency by parasitic elements rotating around the stationary central array.

It will become immediately clear that if the antenna for receiving the interrogation pulses and radiating the position determining signals is mounted on a movable platform the maximum transmission power of an interrogation pulse pair by an aircraft and receipt of a reply pulse pair from the surface beacon varies with movement of the antenna. This introduces errors into the bearing information and distance information.

Heretofore, systems for stabilizing antennas on movable platfonns used powered stabilization devices, i.e., amplifiers, servomotors, gear trains, drives and associated electronic circuitry. These powered stabilization systems, which require electromechanical circuitry and devices, increase the antenna weight and volume and even under the most favorable conditions are complex and unreliable. They require periodic maintenance and consume electric power and are costly. A feature of the present invention is to provide stabilization of an antenna structure with a pendulum-like system.

In one embodiment of the present invention, a motion stabilized antenna structure having a central antenna array includes a supporting yoke having first and second bearings with a common axis aligned to provide stabilization in the desired direction. A pedestal including a mounting plate that has a first journal rotating in the first bearing and a second journal rotating in the second bearing supports a spin motor affixed to the underside of the mounting plate. This spin motor provides a pendulum-like weight to maintain the plate in a substantially horizontal position. A plurality of electromagnetic wave radiation elements mounts to the output shaft of the spin motor above the mounting plate. These radiation elements rotate about the central antenna array modulating signals emitting therefrom.

In accordance with another embodiment of the invention, a motion stabilized antenna structure having a central antenna array includes a support yoke having first and second bearings with a common axis aligned to provide stabilization in the first desired direction. A gimbal ring having extending journals rotates in the bearings of the supporting yoke and has two bearings supported thereon with a common axis aligned to provide stabilization in a second desired direction. A pedestal including a mounting plate has a first journal rotating in one of the bearings of the gimbal ring and a second journal rotating in the second bearing of the gimbal ring. Attached to the underside of the mounting plate is a spin motor that provides a pendulum-like weight to maintain the mounting plate in a substantially horizontal position. Electromagnetic wave radiation elements are mounted to the output shaft of the spin motor above the mounting plate. These radiation elements rotate about the central antenna array.

A more complete understanding of the invention and its advantages will be apparent from the specification and claims and from the accompanying drawings illustrative of the invention.

Referring to the drawings:

FIG. 1 is a pictorial view of a role stabilized radio navigation antenna structure;

FIG. 2 is a pictorial view of the antenna structure of FIG. 1 with the antenna radome and spin motor shroud removed;

FIG. 3 is a cross-sectional view of the stabilized plat form with the spin motor and antenna structure mounted thereto;

FIG. 4 is an enlarged view of the central antenna array of FIG. 3;

FIG. 5 is a top view of an antenna structure stabilized along two orthogonal axis;

FIG. 6 is a side view of the antenna stabilizing system of FIG. 5;

FIG. 7 is a cross-section of an antenna system having a rotating drum supporting parasitic elements for both 15 and Hz modulation revolving about a central antenna array and motion stabilized with a protective radome, this antenna may be roll and pitch stabilized as shown in FIGS. 5 and 6; and

FIG. 8 is a cross-section of a side view of the antenna system of FIG. 7.

Referring to FIGS. 1, 2 and 3, there is shown a radio navigation antenna as used with Distance Azimuth Measuring Equipment (DAME) systems. Typically, such antenna structures are used with radio navigation systems for shipboard installations. In such applications, where the ship has a tendency to roll, it is desirable to orient the antenna structure in a vertical position. The structure must then be motion stabilized along an axis coinciding with the keel of the ship.

The ships mast to antenna adapter 10 is conventionally attached atop the ships mast and the mast attached to the ships super structure. The adapter supports at its upper end a mounting yoke 12 consisting of a base plate 14 and two upstanding end plates 16 and 18. At the top of each of the end plates 16 and 18 there is mounted ball bearings 20 and 22, respectively. These ball bearings have a center axis aligned with the desired axis about which stabilization is desired. For a shipboard installation, the end plate 18 faces the ships bow and the end plate 16 the ship's stem with the axis of the bearings 20 and 22 aligned with the ships keel.

To support the antenna structure 24 in the yoke 12, a pedestal consisting of mounting plate 26 has pivot arm brackets 28 and 30 bolted to the mounting plate. The pivot arm bracket 28 includes a pivot shaft 32 extending through the bearing 20 and rotatable therewith. Similarly, the pivot arm bracket 30 includes a pivot shaft 34 extending through the bearing 22 and rotating therewith. Attached to the underside of the mounting plate 26 is a motor bracket including a lower plate 36 and bracket arms 38 and 40. Secured to the lower plate 36 is a spin motor 42 actuated by power coupled to the antenna structure 24 by means of a cable 44. The spin motor construction may be as described in the copending application of Sidney Pickles et al., Ser. No. 224,783, filed Feb. 9, 1972.

Attached to the rotating member of the spin motor 42 is a flange 46 that has bolted thereto a cylindrical tube 50. Preferably, the cylindrical tube 50 is of a thin dielectric material, such as fiberglass. The tube 50 provides a mounting for parasitic elements 54 and 56 on spaced filaments 58 extending between collars 60. To maintain a spaced relationship between the tube 50 and a central antenna array 62, the upper end of the central array mates with a positioning piece 48a which is fastened to the top underside of the radome 48.

Referring to FIG. 4, the central antenna array 62 connects to the cable 44a through appropriate connectors and includes a main transmission line 64 and a center conductor 66. A secondary transmission line or distribution line 68 is arranged around the main transmission line. This secondary transmission line is provided with radiation skirts 70, 72, 74 and 76. Each of these skirts has a configuration of an open ended cylinder with the skirts 70 and 74 opening upward and the skirts 72 and 76 opening downward.

Energy from a main feed point 78 of the antenna is fed into the secondary transmission line 68 and divided in equal parts in both directions along the main transmission line 64. Equal portions of the energy from the main feed point arrive at the radiation slots 80 and 82 with the skirts 70, 72, 74 and 76 radiating the energy from the antenna. Each of the skirts is substantially one-quarter wavelength long. Energy from the radiation slots 80 and 82 is radiated by the skirts 70, 72, 74 and 76 with each skirt being arranged along the transmission line 68 at one-quarter wavelength intervals.

As constructed, the central antenna array 62 is two stacked dipole elements having a vertically polarized circular radiation pattern. This central antenna array is mounted through the flange 46 in a fixed relationship with the mounting plate 26. As described in the copending application of Sidney Pickles et al., Ser. No. 224,783, this mounting arrangement is provided by having a spin motor 42 with a hollow rotar shaft.

As radiated energy leaves the central array 62 it passes through the cylindrical tube 50 and illuminates the two parasitic elements 54 and 56 which provide a low frequency amplitude modulation to the radiated energy. This radiated energy has a peak main lobe tilted upward above the horizon. The purpose of the uptilt is to reduce the energy that is radiated below the horizon to provide more efficient navigation system operation. This positive angle assures that the major portion of the radiated energy is concentrated at a positive angle (i.e., above the horizon).

An aircraft receiving signals from the antenna will receive a direct ray and also any reflected rays. If the direct ray and the reflected ray arrive in phase at the receiving point, the signals will add, and conversely if the rays arrive out of phase, they subtract and the resultant signal at the receiving point becomes weaker. These areas are called maxima and minima (or nulls). The depth of a null is equal to the energy of the direct ray minus the energy of the reflected ray. If the rays are equal in amplitude and opposite in phase at the receiving point, complete cancellation occurs and the resultant signal is zero. Thus, it is important that as much energy as possible be radiated above the horizon and energy below the horizon be minimized. It is the energy that is radiated from the antenna below the horizon which strikes the earth and is rcradiated to produce a null characteristic.

The antenna array 62 and the parasitic elements 54 and 56 along with the RF components of the structure are designed to provide a maximum uptilt of energy emitted from the antenna structure. For a rigidly mounted antenna on a rolling platform, the main lobe of the radiated energy may dip below the horizon and interrogating aircraft may lose contact with the navigation system. An important feature of the present invention is mounting of the antenna structure including the spin motor 42 on a rotating mounting plate 26 to maintain the main lobe energy always above the horizon.

As illustrated, the pedestal including the mounting plate 36 and the brackets 38 and 40 along with the spin motor 42 act as a pendulum-like weight to maintain the mounting plate 26 in a substantially horizontal orientation.

To minimize the effects of wind loading and to protect the antenna parts a radome 48 is mounted to the upper surface of the mounting plate 26 and encloses the antenna proper, also the spin motor 42 is enclosed in a shroud 84. Both the radome 48 and the shroud 84 are configured to have substantially the same windage factor. Thus, for a given wind velocity at the radome 48 and the shroud 84, equal but opposite moments of rotation will be generated at the pivot shafts 32 and 34. This further assures maintaining a proper vertical orientation 0f the antenna structure to insure maximum energy distribution above the horizon.

To tailor the motion stabilizing effect of the pendulum mounted antenna structure for particular roll conditions, an adjustable dashpot 92 is mounted to the end plate 16 and includes a shaft member 88 coupled to an extension 90 of the pivot shaft 32. The amount of dampening effect on the mounting plate 26 is adjustable by means of a knob 92 that varies the drag on the extension 90 as transmitted through the member 88.

Also assembled to rotate with the mounting plate 26 is a monitor antenna 94 which connects to the system transponder through the cable 44b. The monitor antenna 94 provides means for checking the operation of the antenna 24.

In the operation of TACAN (DAME) navigation systems, high frequency reference trigger bursts are used for synchronizing the system operation. One technique used for generating these frequency bursts employs an infrared detector 96 which when operated in conjunction with a light interrupting disc 98 creates timing pulses synchronized with rotation of the parasitic elements 54 and 56. The interrupting disc 98 is mounted to the shaft of the spin motor 42 and rotates with the parasitic elements 54 and 56.

For platforms such as large ships where normally the only requirements for antenna stabilization is along a roll axis, the apparatus of FIGS. 1-4 provide the required stabilization of the antenna structure in a vertical direction. When the antenna platform has instability in more than one direction, compensation along two axis is required.

Referring to FIGS. 5 and 6, there is shown a modification of the apparatus of FlGS. 1-4 for maintaining the mounting plate 26 in a substantially horizontal orientation when the mounting yoke 12 may be unstable along more than one axis. When referring to the same elements, the same reference numerals will be used in the description of the apparatus of FIGS. 5 and 6.

The mounting yoke 12 includes a base plate 14 and upstanding end plates 16 and 18. Mounted to the top portion of the end plates 16 and 18 are bearings 20 and 22, respectively, with an axis aligned to provide stabilization in a direction coinciding with a first desired direction. A gimbal ring 100 has extending from one side thereof a pivot shaft 102 engaging the bearing 20 and rotating therewith. A second pivot shaft 104 also extends from the gimbal ring 100 and engages the bearing 22 for rotation therewith. As mounted, the gimbal ring 100 rotates about an axis coinciding with the first direction of desired stabilization.

Along an axis orthogonal to the axis of the pivot shafts 102 and 104 there is mounted on the gimbal ring 100 ball bearings 106 and 108. The mounting plate 26, having pivot arm brackets 28 and 30 attached thereto, rotates about an axis coinciding with the axis of the bearings 106 and 108. This axis is aligned to provide stabilization along a second desired direction. Extending from the pivot arm bracket 28 is a pivot shaft 32 that engages the bearing 106 and rotates therein. Similarly, the pivot arm bracket 30 has extending therefrom a pivot shaft 34 that engages the bearing 108 to rotate therewith.

Attached to the underside of the mounting plate 26 is a pedestal supporting the spin motor 42 (not shown in FIGS. 5 and 6) within the shroud 84. Above the mounting plate 26, as illustrated in FIG. 1, there is mounted the radome .48 enclosing the antenna structure including the central antenna array 62 and the rotating parasitic elements 54 and 56.

With the apparatus as described, the antenna structure secured to the mounting plate 26 is stabilized in a substantially vertical position by maintaining the mounting plate 26 in a substantially horizontal position. The gimbal ring provides stabilization of the mounting plate 26 for movement of the yoke 12 in a direction along an axis coinciding with the pivot shafts 102 and 104. For a movement of the mounting yoke 12 along an axis coinciding with the pivot shafts 32 and 34, the bearings 106 and 108 allow the mounting plate 26 to be maintained in a substantially horizontal orientation.

Mounted to the end plate 16 is a dashpot 86 as described with reference to FIGS. 1 and 2. This dashpot provides a dampening effect to the gimbal ring 100. Mounted to the gimbal ring 100 is a dashpot 110 similar to the dashpot 86. The dashpot 110 includes a member 112 in engagement with the pivot shaft 34. This provides a dampening effect to the mounting plate 26 for movement in a direction coinciding with the pivot shafts 32 and 34.

'To lock the mounting plate 26 and the gimbal ring 100 /in a fixed position with relationship to the bottom plate 14, an anti-roll bracket 114 is fastened to the lower plate 36 and an anti-roll bracket 116 is fastened to the gimbal ring 100. A solenoid bracket 118 mounts to the base plate 14 and supports a solenoid 120 that drives a pin into an opening of the anti-roll bracket 114 to hold the plate 26 in a fixed position with relation to the base plate 14. A similar solenoid bracket 122 also mounts to the base plate 14 and supports a solenoid 124 that drives a locking pin through an opening of the anti-roll bracket 116. This locks the gimbal ring 100 in a fixed position.

For improved system accuracy, a group of additional parasitic elements, mounted a fixed number of degrees 5 apart, also rotate around the central antenna array 62 along with the low frequency parasitic elements 54 and 56 and further modify the cardioid radiation pattern. Although the cardioid pattern is still predominant, it is altered by superimposed ripples. The interrogating aircraft now receives the low frequency modulation with a higher frequency ripple amplitude modulated on the distance data reference pulses. To furnish a suitable reference for measuring the phase of the high frequency components of the envelope waves, a coded high frequency reference signal pulse is transmitted from the beacon transponder.

Referring to FIGS. 7 and 8, there is shown a pendulum stabilized antenna structure having high frequency and low frequency parasitic elements revolving about a stationary central antenna array. Although described with reference to a ship as the supporting platform, it will be understood that the stabilization apparatus as described may also be employed on platforms other than ships.

A portion of the ships mast 126 is shown having a flange bolted or otherwise secured to a mounting yoke 128 including a base plate 130 and upstanding end plates 132 and 134. As shown in FIG. 7, the mounting yoke 128 is oriented such that the end plate 132 faces the ship's bow and the end plate 134 faces the ships stern. In the upper portion of the end plates 132 and 134 there is mounted ball bearings 136 and 138, respectively. Supported in the ball bearing 136 is a pivot shaft 140 extending from a pivot arm bracket 142 bolted to an upper pedestal plate 144. Similarly, the bearing 138 supports a pivot shaft 146 extending from a pivot arm bracket 148 bolted to the upper pedestal plate 144. With the axis of the pivot shafts 140 and 146 aligned along a desired direction of stabilization, such as the keel of a ship, the upper pedestal plate 144 will rotate freely about this axis in the bearings 136 and 138.

Bolted to the underside of the plate 144 are brackets 150 having a lower pedestal plate 152 secured thereto. A spin motor bracket 154 also bolts to the underside of the plate 144 and supports a spin motor 156 in a pendulum-like weight below the plate 144.

Attached to the rotating shaft of the spin motor 156 is a flange 158 that supports a rotating drum 160. As mentioned previously, preferably the rotating drum is of a thin dielectric material. It is a spiral wound support on which there is mounted nine split sets of high frequency parasitic elements 162 (only one set shown) such as described in the copending application of Sidney Pickles et 211., Ser. No. 224,783. The nine parasitic elements 162 are spaced around the drum at 40 intervals, and, in the embodiment shown, are adhered to the outside surface with an adhesive.

Also rotating with the drum 160 is a support tube 164 by means of a collar 168. The support tube 164 supports the split low frequency parasitic elements (only one set shown) on spaced filaments 172 extending between collars 174. Enclosing the entire assembly of the support tube 164 and the parasitic elements 170 is a guard 176 of a thin dielectric material. To maintain a spaced relationship between the drum 160 and the tube 164, the upper end of the tube is fitted with a positioning ring 178 fastened to the upper wall of the drum 160. Secured to this positioning ring are selectable balance weights 180 that are chosen to provide an equal weight balance between the structure above the upper pedestal plate 144 and the equipment below the plate 144.

The central antenna array 62 as shown in FIG. 4 connects to a coaxial cable 182 through a connector 184 at the lower pedestal plate 152. The central antenna array 62 is stationary mounted with respect to the upper pedestal plate 144 and may extend through the hollow rotor shaft of the spin motor 156. At the upper end of the antenna array 62 there is positioned a bearing 186 that includes an outer race press fit into the positioning ring 178. This maintains the spaced relationship between the central antenna array 62 and the rotating parasitic elements 162 and 170.

The central antenna array 62 and the parasitic elements 162 and 170 along with the entire supporting structure are enclosed within a radome 188 comprising an upper half 188a fastened to a lower half 1881: to form a weather tight enclosure. This enclosure is bolted to the base plate 130 and is fixed in position with respect to the ships mast 126. As shown specifically in FIG. 8, as the ship rolls the entire antenna structure as supported by the pivot arms 142 and 148 rotates with respect to the mounting yoke 128 within the radome 188. In this configuration, the spin motor 156 need not be enclosed within a shroud and windage has a minimal effect on the orientation of the antenna because of the protective enclosure formed by the radome 188.

Mounted to the etd plate 134 is an adjustable dashpot 190 coupled to the shaft 146 and including an adjusting knob 192. The dashpot 190 may be the same as the dashpot 86 as illustrated in FIGS. 1 and 2.

As the main antenna structure rotates with. respect to the mounting yoke 128, a monitor antenna 194 rotates therewith. The monitor antenna 194 includes a counterpoise 196, all supported on a bracket 198 clamped to the pivot shaft 140. This arrangement enables the monitor antenna to be maintained in a fixed position with respect to the main antenna structure.

To lock the antenna structure in a fixed position with respect to the mounting yoke 128, an anti-roll bracket 200 is attached to the lower pedestal plate 152. A second anti-roll bracket 202 is mounted to the base plate 130 and supports a solenoid 204 that drives a locking pin into the bracket 200 for maintaining the antenna structure in a fixed position. This arrangement is similar to that previously described in FIG. 6. It should be understood, that the locking mechanisms described herein are only exemplary and numerous other such locking devices, including manually operated locks, may be employed.

While several embodiments of the invention, together with modifications thereof, have been described in detail herein and shown in the accompanying drawings, it will be evident that various further modifications are possible without departing from the scope of the invention.

What is claimed is:

l. A pendulum stabilized antenna structure having radiation elements for rotation about a central antenna array, comprising in combination:

a support having first and second bearings with a common axis aligned to provide stabilization in the desired direction,

a pedestal including a mounting plate having first and second pivot shafts extending therefrom, the first shaft rotating in the first bearing and the second shaft rotating in the second bearing,

dampening means attached to said support and direct coupled to one of the pivot shafts of said mounting plate for retarding the motion of said plate,

a spin motor affixed to the underside of the mounting plate and having an output shaft coupled to the radiating elements, said motor providing a pendulum-like weight to maintain said mounting plate in a substantially horizontal position,

a radome with a predetermined windage factor enclosing the central antenna array, and

a shroud having substantially the same windage factor as said radome and enclosing the spin motor, said radome and said shroud providing substantially the same windage resistance above and below the pivot shaft of said mounting plate.

2. A pendulum stabilized antenna structure having radiation elements for rotation about a central antenna array, comprising in combination:

a support having first and second bearings aligned along a common axis in a direction of desired stabilization,

a pedestal including a mounting plate having first and second pivot shafts extending therefrom, the first pivot shaft rotating in the first bearing and the second shaft rotating in the second bearing of said support,

a spin motor affixed to the underside of the mounting plate and having an output shaft coupled to the radiating elements, said motor providing a pendulum-like weight to maintain said mounting plate in a substantially horizontal position,

a radome having a predetermined windage factor enclosing the central antenna array and the radiation elements, said radome attached to the mounting plate opposite said spin motor, and

a shroud having substantially the same windage factor as said radome and enclosing the spin motor and attached to said mounting plate on the side opposite said radome, said radome and said shroud providing substantially the same windage plate.

3. A pendulum stabilized antenna structure as set forth in Claim 2 including an adjustable dashpot attached to said support and having an output shaft direct coupled to one of the pivot shafts of said mounting plate for retarding the motion of said plate.

4. A motion stabilized antenna structure as set forth in claim 3 including means for locking said mounting plate in a fixed position with respect to said support.

5. A pendulum stabilized antenna structure having radiation elements for rotation about a central antenna array, comprising in combination:

a support having first and second bearings aligned along a common axis in a direction of desired stabilization,

a gimbal ring having first and second pivot shafts extending therefrom and including third and fourth bearings aligned along a common axis to provide stabilization in a second desired direction, the first shaft rotating in the first bearing and the second shaft rotating in the second bearing of said support, a pedestal including a mounting plate having first and second pivot shafts extending therefrom, the first shaft rotating in the third bearing and the second shaft rotating in the fourth bearing,

a spin motor affixed to the underside of the mounting plate and having an output shaft coupled to the radiating elements, said motor providing a pendulum-like weight to maintain said mounting plate in a substantially horizontal position,

a radome having a predetermined windage factor enclosing the central antenna array and the radiation elements, said radome attached to the mounting plate opposite said spin motor, and

a shroud having substantially the same windage factor as said radome and enclosing the spin motor and attached to said mounting plate on the side opposite said radome, said radome and said shroud providing substantially the same windage resistance above and below the pivot shaft of said mounting plate.

6. A pendulum stabilized antenna structure as set forth in claim including an adjustable dashpot attached to said support and having an output shaft direct coupled to one of the pivot shafts of said gimbal ring for retarding the motion of said ring.

7. A pendulum stabilized antenna structure as set forth in claim 6 including a second adjustable dashpot attached to said gimbal ring and having an output shaft direct coupled to one of the pivot shafts of said mounting plate for retarding the motion of said plate.

8. A motion stabilized antenna structure as set forth in claim 5 including means for locking said gimbal ring and said mounting plate in a fixed position with respect to said support.

9. A motion stabilized antenna structure as set forth in claim 5 including a second plurality of radiation elements mounted to the output shaft of the spin motor for rotation about the central antenna array and the first plurality of radiation elements to provide a second modulating frequency to radiation emitting from said array.

UNITED STA'IES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3 ,789 ,414 v v Dated January 29 1974 Inventor s e g Bauer and Dean S. Thornberg It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet should read as follows:

-- PENDULUM STABILIZATION FOR ANTENNA STRUCTURES WITH RADO1 [E--,-

Col. 3 line 44, "rotar" should be -rotor--.

Col. 5, line 58, "/in" should be --in-- Col. 7, line 32, "etd" should be -end--.

Col. 8, line 45, after "windage" insert --resistance above and below the pivot shaft of said mounting-- Signed and sealed this 6th day of August 1974.

(SEAL) Attest:

McCOY M. GIBSON C. MARSHALL DANN Attesting Officer Commissioner of Patents 

1. A pendulum stabilized antenna structure having radiation elements for rotation about a central antenna array, comprising in combination: a support having first and second bearings with a common axis aligned to provide stabilization in the desired direction, a pedestal including a mounting plate having first and second pivot shafts extending therefrom, the first shaft rotating in the first bearing and the second shaft rotating in the second bearing, dampening means attached to said support and direct coupled to one of the pivot shafts of said mounting plate for retarding the motion of said plate, a spin motor affixed to the underside of the mounting plate and having an output shaft coupled to the radiating elements, said motor providing a pendulum-like weight to maintain said mounting plate in a substantially horizontal position, a radome with a predetermined windage factor enclosing the central antenna array, and a shroud having substantially the same windage factor as said radome and enclosing the spin motor, said radome and said shroud providing substantially the same windage resistance above and below the pivot shaft of said mounting plate.
 2. A pendulum stabilized antenna structure having radiation elements for rotation about a central antenna array, comprising in combination: a support having first and second bearings aligned along a common axis in a direction of desired stabilization, a pedestal including a mounting plate having first and second pivot shafts extending therefrom, the first pivot shaft rotating in the first bearing and the second shaft rotating in the second bearing of said support, a spin motor affixed to the underside of the mounting plate and having an output shaft coupled to the radiating elements, said motor providing a pendulum-like weight to maintain said mounting plate in a substantially horizontal position, a radome having a predetermined windage factor enclosing the central antenna array and the radiation elements, said radome attached to the mounting plate opposite said spin motor, and a shroud having substantially the same windage factoR as said radome and enclosing the spin motor and attached to said mounting plate on the side opposite said radome, said radome and said shroud providing substantially the same windage plate.
 3. A pendulum stabilized antenna structure as set forth in Claim 2 including an adjustable dashpot attached to said support and having an output shaft direct coupled to one of the pivot shafts of said mounting plate for retarding the motion of said plate.
 4. A motion stabilized antenna structure as set forth in claim 3 including means for locking said mounting plate in a fixed position with respect to said support.
 5. A pendulum stabilized antenna structure having radiation elements for rotation about a central antenna array, comprising in combination: a support having first and second bearings aligned along a common axis in a direction of desired stabilization, a gimbal ring having first and second pivot shafts extending therefrom and including third and fourth bearings aligned along a common axis to provide stabilization in a second desired direction, the first shaft rotating in the first bearing and the second shaft rotating in the second bearing of said support, a pedestal including a mounting plate having first and second pivot shafts extending therefrom, the first shaft rotating in the third bearing and the second shaft rotating in the fourth bearing, a spin motor affixed to the underside of the mounting plate and having an output shaft coupled to the radiating elements, said motor providing a pendulum-like weight to maintain said mounting plate in a substantially horizontal position, a radome having a predetermined windage factor enclosing the central antenna array and the radiation elements, said radome attached to the mounting plate opposite said spin motor, and a shroud having substantially the same windage factor as said radome and enclosing the spin motor and attached to said mounting plate on the side opposite said radome, said radome and said shroud providing substantially the same windage resistance above and below the pivot shaft of said mounting plate.
 6. A pendulum stabilized antenna structure as set forth in claim 5 including an adjustable dashpot attached to said support and having an output shaft direct coupled to one of the pivot shafts of said gimbal ring for retarding the motion of said ring.
 7. A pendulum stabilized antenna structure as set forth in claim 6 including a second adjustable dashpot attached to said gimbal ring and having an output shaft direct coupled to one of the pivot shafts of said mounting plate for retarding the motion of said plate.
 8. A motion stabilized antenna structure as set forth in claim 5 including means for locking said gimbal ring and said mounting plate in a fixed position with respect to said support.
 9. A motion stabilized antenna structure as set forth in claim 5 including a second plurality of radiation elements mounted to the output shaft of the spin motor for rotation about the central antenna array and the first plurality of radiation elements to provide a second modulating frequency to radiation emitting from said array. 